Filter Device

ABSTRACT

The invention relates to a filter device, especially a line filter forming part of hydraulic installations, said filter device comprising a filter housing ( 1 ) that can be removed from a filter head and is used to receive a filter element ( 5 ) that separates a non-filtered side ( 13 ) from a filtered side ( 11 ) in a position in the filter housing for the operation of the filter. According to the invention, the filter device is provided with a display device ( 19, 21 ) signalling the absence or presence of the filter element ( 5 ) in the filter housing ( 1 ) in the operating position.

The invention relates to a filter device, especially a line filter which forms a component of hydraulic systems, with a filter housing which can be removed from a filter head and which is used to hold a filter element which separates the unfiltered side from the filtered side when the operating position for filter operation has been assumed in the filter housing.

Filter devices of this type are known, cf. Der Hydrauliktrainer, Band 1, 1991 [Hydraulics Training Manual, Volume 1, 1991], published by Mannesmann Rexroth GmbH, pp. 279 and 280. Filter devices such as these can be designed for operation with so-called spin-on cartridges, it being possible for the filter cartridge, which contains a filter element permanently installed in the housing, to be screwed onto the filter head, and after expiration of the useful operating time of the filter element its being replaced such that the entire cartridge with the used filter element contained therein is disposed of. On the other hand, filter devices such as these can also be operated in a design in which a filter housing with a filter element, which can be held interchangeably therein, is removably attached to the filter head so that when the filter element is changed, only the latter is removed from the filter housing and disposed of, and the filter housing provided with a new filter element continues to be used.

It is apparent that the latter design is comparatively more advantageous with respect to conservation of resources and the resulting operating costs due to the continued use of the filter housing. On the other hand, the design in which so-called spin-on cartridges are used is characterized by especially high operating reliability, because the fixed installation of the filter element in the housing of the spin-on cartridge avoids the danger that in the course of replacement of a used filter element an empty filter housing without the fresh filter element inserted into it will be unintentionally attached to the filter head. On the other hand, in filter devices with a reusable filter housing serious damage or even destruction of the pertinent hydraulic system can occur if a filter housing without the filter element located therein is inadvertently attached to the filter head, for example through the carelessness of the operator only a used filter element being selected and insertion of a fresh element being omitted.

On the basis of this prior art, the object of the invention is to devise a filter device in which the danger that the hydraulic system which is assigned to the device will be operated without a filter element in the filter housing is avoided.

According to the invention, this object is achieved by a filter device which has the features of claim 1 in its entirety.

In that according to the invention there is a display device which indicates the presence or absence of the filter element which is located in the filter housing in the operating position, the danger of faulty operation of the filter device without an inserted filter element is avoided. Thus, in this respect a uniform measure of operating reliability is achieved, as is the case in the design in which so-called spin-on cartridges are used, for which the filter element together with the cartridge housing which contains it is replaced. But in the invention the disadvantages of wasting material and the increased operating costs as prevail when using spin-on cartridges are avoided.

In preferred embodiments, the display device in the wall of the filter housing has an opening and a closing means which depending on the presence or absence of a filter element in the operating position can be moved into the open state which clears the opening or a blocked state which closes the opening so that clearance or closure of the opening indicates the presence or absence of a filter element. Since as a result of the cleared opening of the filter housing fluid emerges from the filter housing when the filter device is operated without the filter element inserted, the fault state is immediately indicated and the pertinent hydraulic systems can be prevented from being operated in the fault state.

In one preferred embodiment the closing means has at least one closing body with at least one sealing element which in the operating position of the filter element forms a seal between the closing body and the opening, the closing body being formed by a bearing part of the filter element which is held in a seat of the filter housing in the operating position. Because in this connection the bearing part of the filter element which interacts with the seat of the filter housing also acts as a closing body of the closing means and thus as a component of the display means, the design is especially simple, compact and economical.

The bearing part of the filter element can be advantageously formed by an extension on the end of its support tube which bears the filter material and which in the operating position is held in the seat of the filter housing which is formed by a pipe socket-like depression in the bottom of the filter housing which concentrically surrounds the opening, on the outside of the bearing part there being the sealing element of the closing means which interacts with the inside wall of the seat of the filter housing which surrounds the opening to form a seal.

Since in filter operation axial forces which act in the direction of the longitudinal axis of the support tube can occur on the filter element, it is advantageous to safeguard the bearing part which is formed by the axial extension of the support tube against lifting caused by axial forces out of the seat of the filter housing. For this purpose the bearing part of the support tube can have a hole with an inside thread which is flush with the opening of the filter housing in the operating position, so that the bearing part and thus the filter element can be axially locked in the filter housing by a retaining screw which extends through the opening of the filter housing.

This hole of the bearing part can be made continuous into the interior of the support tube, that is, as far as the filtered side, the closing means having another sealing element which seals the edge of the opening on the outside of the filter housing relative to the head of the retaining screw. In this way even when the filter element is in the operating position, if necessary, the filtered side can be emptied by loosening the retaining screw and taking it out of the hole.

In one development of such an embodiment the bearing part can have at least one connecting channel which enables a connection between the continuous hole and the unfiltered side in the filter housing, and which channel can be closed by the unthreaded shaft section and which can be cleared by unscrewing the retaining screw. This also enables emptying of both the filtered side and also the unfiltered side as needed when the filter element is in the operating position.

If in this embodiment a partial segment of the hole which passes through the bearing part has a widening which forms a fluid passage between the end region facing the opening of the filter housing and the region of the hole which can be closed by the unthreaded shaft section of the retaining screw, for purposes of emptying of both the filtered side and also the unfiltered side with the filter element in the operating position the retaining screw need simply be loosened, but not removed entirely from the hole.

However the configuration can also be such that the retaining screw has an inner longitudinal channel which is open on its end facing the interior of the filter housing and which is opened by way of a transverse outlet on its opposite end in the shaft region which adjoins the sealing element which seals the head of the retaining screw. In this case as well, without having to remove the retaining screw completely from the hole, it is possible to empty both the filtered side and also the unfiltered side when the filter element is in the operating position.

To ensure that the unscrewed retaining screw remains captively on the filter housing, the configuration can be such that the head of the retaining screw on the end facing away from the shaft has a driving part with radially extending driver blades which are guided in a rotary cage which is supported on the filter housing to be rotatable and axially nondisplaceable around the axis of the screw in a guide which has stops for transmission of the torque to the screw and at least one stop for limiting the axial motion of the screw when it is loosened.

The subject matter of the invention is also a filter element for the device according to the invention which has the features of claim 11 in its entirety.

The invention will be detailed below using embodiments which are shown in the drawings.

FIG. 1 shows a cutaway perspective showing only the lower partial region in a first embodiment of the filter device according to the invention, cut with cutting planes which run in the longitudinal direction of the filter housing and at a right angle to one another and

FIGS. 2 to 4 show representations of other embodiments of the filter device according to the invention similar to FIG. 1.

A filter housing 1, of which in the figures only the region adjacent to the housing bottom 3 is shown, can be connected in the manner which is known in these filter devices with its end which is open to the top and which is not shown, to a filter head, for example by screwing it in. The filter head has connection means for feed and discharge of the fluid to be filtered and optionally accessory means, for example a connection for clogging indicators and the like. In the interior of the filter housing 1 which is shaped to be circularly cylindrical over a large part of its length a filter element designated as a whole as 5 can be held; it is shown in the figure continuously in its operating position. The filter element 5 has a fluid-permeable support tube 7 which is surrounded by the filter material 9. The upper end of the support tube 7 which is not shown is tightly connected on the filter head to the outlet for the filtered fluid, while the fluid to be filtered travels from the feed of the filter head to the outside of the filter material 9. Thus the interior of the support tube 7 in filter operation forms the filtered side 11, while the space surrounding the filter material 9 within the filter housing 1 forms the unfiltered side 13.

As the seat in which the filter element 5 in its operating position is held within the filter housing 1, the bottom 3 of the filter housing 1 has a centrally located, pipe socket-like depression 15 with an inside wall 17 which is concentric to the opening 19 which is centrally positioned on the base of the depression 15 and flush with the longitudinal axis of the support tube 7.

A metallic extension of the support tube 7 which projects on the lower end of the support tube 7 concentrically to its longitudinal axis forms a circularly cylindrical bearing part 21. The latter in the operating position of the filter element 5 is held in a depression 15 which forms the seat, a sealing element 23 which sits on the outside of the bearing part 21 in an annular groove sealing the bearing part 21 relative to the inside wall 17 of the depression 15 and thus relative to the opening 19 which is located on the base of the depression 15. The bearing part 21 thus forms a closing means which blocks discharge of fluid from the unfiltered side 13 out of the opening 19 when the filter element 5 is in the operating position. Since the bearing part 21 seals the lower end of the support tube 7 fluid-tight, fluid cannot emerge from the filtered side via the opening 19. On the other hand, the opening 19 is opened when a filter element 5 is not present, so that with improper start-up with the filter element 5 missing, this impermissible operating state is indicated by escape of fluid through the opening 19.

The embodiment of FIG. 2 differs from the example of FIG. 1 simply in that the bearing part 21 of the filter element 5 is not made entirely as a hollow body which has only a thin-walled bottom, but that the bearing part 21 of FIG. 2 has an internal solid core in which a hole 33 with an inside thread 25 is formed into which a retaining screw 27 can be screwed with a head 29 which adjoins the outside of the housing. The retaining screw 27 safeguards the bearing part 21 and thus the filter element 5 in the operating position against axial forces which could occur in filtering operation on the filter element 5 so that it is ensured that an annular shoulder 31 which projects radially on the bearing part 21 in contact with the assigned stop surface which forms a radial widening on the inside wall 17 of the depression 15 is safeguarded.

In contrast to the example of FIG. 2, in the bearing part 21 of the filter element 5 there is a through hole 33 via which a fluid connection between the filtered side 11 within the support tube 7 and the opening 19 on the base of the depression 15 can be produced when the filter element 5 is in the operating position. Moreover, by way of the connecting channel 35 which running crosswise in the bearing part 21 connects the hole 33 to the unfiltered side 13 within the filter housing 1, the hole 33 enables the unfiltered side 13 to be emptied when the filter element 5 is in the operating position. As is to be seen in FIG. 3, the retaining screw 27 which is provided in this embodiment has an end-side, unthreaded shaft section 37 which closes the inner end of the connecting channel 35, with the retaining screw 27 screwed tight, as is shown in FIG. 3. As is likewise to be seen in FIG. 3, the hole 33 on the longitudinal segment proceeding from the free end of the bearing part 21 has a widening 39 in the form of a groove which interrupts the inner thread 25 only on a small peripheral segment and which enables a fluid connection via the hole 33 to the housing opening 19 even when the retaining screw 27 has not been completely unscrewed from the hole 33, that is, when there is still engagement with the end region of the inner thread 25. Thus, with the filter element 5 in the operating position with the retaining screw 27 partially screwed out, when the opening 19 is no longer sealed by another sealing element 41 which, when the retaining screw 27 has been tightened, seals its screw head 29 relative to the outside edge of the opening 19, the filtered side 11 and the unfiltered side 13 can be emptied as soon as the retaining screw 27 has been unscrewed so far that its unthreaded shaft section 37 moves into the region of the widening 39 of the hole. In any case, the retaining screw 27 can be completely unscrewed, i.e., removed. As in the examples of FIGS. 1 and 2, when there is no filter element 5 in the filter housing 1, the housing opening 19 is not closed so that in turn possible faulty operation is indicated by escape of fluid from the filter housing 1.

The example of FIG. 4 differs from the example of FIG. 3 in two respects. FIG. 4 shows the filter element 5 in its operating position, but with the retaining screw 27 partially unscrewed. The first major difference relative to the example of FIG. 3 consists in that the retaining screw 27 has an inner longitudinal channel 43 which extends from the free shaft end 45 up to a transverse outlet 47 which is located at a location of the shaft of the screw 27 which is adjacent to the sealing element 41 to which a seal is formed between the screw head 29 and the outside of the housing on the opening 19, with the screw 27 tightened. In the operating state shown in FIG. 4 with the screw 27 partially released, although the filter element 5 is in the operating position, both the filtered side 11 and also the unfiltered side 13 can be emptied via the connecting channel 35, the inner channel 43 of the screw and its transverse outlet 47. As in the other embodiments, when the filter element 5 is missing in the filter housing 1, the housing opening 19 cannot be closed so that a faulty operating state is indicated in turn by escape of the fluid.

The second fundamental difference relative to the example of FIG. 3 consists in that the retaining screw 27 is captively secured. For this purpose, on the lower end of the housing depression 15 there is a rotary cage 51 which is secured by a snap connection in an annular groove 49, in the form of a cap-like molded piece, preferably of plastic, which on the end facing away from the snap connection has a bottom 53 with an outlet opening 55. The head 29 of the retaining screw 27 on the end side has a driving part 57 with radially projecting driver blades 59 which engage the inner guides 61 of the cage 51 and are guided to be axially displaceable therein, but nonrotatable. The bottom 53 of the cage forms a stop which limits the axial motion of the retaining screw 27 when being screwed out, such that the screw 27 can be screwed out only to the extent that engagement of the thread with the inside thread 25 of the hole 33 is cancelled so that the filter element 5 can be removed from the filter housing 1 and a fresh filter element 5 can be inserted into the operating position. As is shown in FIG. 4, when the filter element 5 is in the operating position both the filtered side 11 and also the unfiltered side 13 can be emptied via the partially unscrewed screw 27, however with the screw 27 being held captively on the housing by the rotary cage 51.

As in the preceding examples, fluid-tight closure of the housing opening 19 is possible only when the filter element 5 is in the operating position so that faulty operation is indicated in turn by the fluid's running out. 

1. Filter device, especially a line filter which forms a component of hydraulic systems, with a filter housing (1) which can be removed from a filter head and which is used to hold a filter element (5) which separates the unfiltered side (13) from the filtered side (11) when the operating position for filter operation has been assumed in the filter housing (1), characterized in that there is a display device (19, 21) which indicates the presence or absence of the filter element (5) which is located in (1) in the operating position.
 2. The filter device according to claim 1, wherein the display device in the wall (15) of the filter housing (1) has an opening (19) and a closing means (21) which depending on the presence or absence of a filter element (5) which is in the operating position can be moved into the open state which clears the opening (19) or a blocked state which closes the opening (19) so that clearance or closure of the opening (19) indicates the presence or absence of a filter element (5).
 3. The filter device according to claim 2, wherein the closing means has at least one closing body with at least one sealing element (23) which in the operating position of the filter element (5) forms a seal between the closing body and the opening (19), and wherein the closing body is formed by a bearing part (21) of the filter element (5), which bearing part (21) is held in a seat (15) of the filter housing (1) in the operating position.
 4. The filter device according to claim 3, wherein the bearing part (21) of the filter element (5) is formed by an extension on the end of its support tube (7) which bears the filter material (9) and which in the operating position is held in the seat (15) of the filter housing (1) which is formed by a pipe socket-like depression (15) in the bottom (3) of the filter housing (1) which concentrically surrounds the opening (19), and wherein on the outside of the bearing part (21) there is a sealing element (23) of the closing means which interacts with the inside wall (17) of the seat (15) of the filter housing (1) which surrounds the opening (19) to form a seal.
 5. The filter device according to claim 4, wherein the bearing part (21) of the support tube (7) has an internally threaded hole (33) which is flush with the opening (19) of the filter housing (1) in the operating position and wherein the bearing part (21) and thus the filter element (5) can be axially locked in the filter housing (1) by a retaining screw (27) which extends through the opening (19) in the filter housing (1).
 6. The filter device according to claim 5, wherein the hole (33) of the bearing part (21) is made continuous into the interior of the support tube (7), and wherein the closing means has another sealing element (41) which seals the edge of the opening (19) on the outside of the filter housing (1) relative to the head (29) of the retaining screw (27).
 7. The filter device according to claim 6, wherein the bearing part (21) has at least one connecting channel (35) which enables a connection between the continuous hole (33) and the unfiltered side (13) in the filter housing (1) and which channel can be closed by the unthreaded shaft section (37) of the retaining screw (27) and which can be cleared by unscrewing the retaining screw (27).
 8. The filter device according to claim 7, wherein a partial segment of the hole (33) which passes through the bearing part (21) has a widening (39) which forms a fluid passage between the end region facing the opening (19) of the filter housing (1) and the region of the hole (33) which can be closed by the unthreaded shaft section (37) of the retaining screw (27).
 9. The filter device according to claim 7, wherein (27) has an inner longitudinal channel (43) which is open on its end facing the interior of (1) and which is opened by way of a transverse outlet (47) on its opposite end in the shaft region which adjoins the sealing element (41) which seals the head (29) of the retaining screw (27).
 10. The filter device according to claim 5, wherein the head (29) of the retaining screw (27) on the end facing away from the shaft has a driving part (57) with radially extending driver blades (59) which are guided in a rotary cage (51) which is supported on the filter housing (1) to be rotatable and axially nondisplaceable around the axis of the screw (27) in a guide (61) which has stops for transmission of the torque to the screw (27) and at least one stop (53) for limiting the axial motion of the screw (27) when it is loosened.
 11. Filter element for a filter device according to claim 1, wherein it has a closing means with a closing body with at least one sealing element (23), which closing body is formed by a bearing part (21) of the filter element (5) which in the operating position of the filter element can be held in a seat (15) of the pertinent filter housing (1) in which there is an opening (19) which can be closed by the sealing element (23) of the bearing part (21) which has been inserted into the seat (15). 